6.9 IDI dies off throttle and weak at idle

[IDIBRONCO]

So maybe I should remove the timing cover and check the gear alignment to see where the mark is if I can't find any other issues?

I'd lean toward that being a last resort. If it was me, I'd remove the front engine cover first. It's underneath the water pump. Others may say different, and I'm not saying that it's the way to do it, but I don't trust myself to get the marks lined up without being able to see them. I also don't trust myself to be able to see if it's a dot or a "Y" that I'm feeling. There's one of each. People will say that you can use a mirror to see whether it's a dot or a Y. Maybe they're right. I've never tried.